Chlorinated polyolefins and process for their production

ABSTRACT

Uniform chlorinated polyolefins which can give crosslinked rubbers and thermoplastic elastomers with excellent low-temperature rubber elasticity, compression set and fatigue strength, and a process for their production. Polyolefin powder pulverized to a mean particle size of no greater than 500μ is used for chlorination.

CROSS-REFERENCE TO RELATED APPLICATION

This application is an application filed under 35 U.S.C. § 111(a)claiming benefit pursuant to 35 U.S.C. § 119(e)(1) of the filing date ofthe Provisional Application 60/412,793 filed Sep. 24, 2002, pursuant to35 U.S.C. § 111(b).

TECHNICAL FIELD

The present invention relates to chlorinated polyolefins and to aprocess for their production. In particular, the invention relates tochlorinated polyolefins which are suitable as starting materials forcrosslinked rubber and thermoplastic elastomer having not only excellentoil resistance, heat resistance and the like, but also excellentlow-temperature rubber elasticity and compression set, and to a processfor their production.

BACKGROUND ART

Chlorinated polyolefins are chlorinated compounds obtained bychlorination of polyolefins such as polyethylene. Chlorinatedpolyolefins are commonly used as modifiers for ABS resins or polyvinylchloride resins or as wire sheaths, but in recent years they are alsocoming into wider use as crosslinked rubbers or thermoplastic elastomersfor automobile parts and industrial parts.

Because of the oil resistance, solvent resistance, weather resistanceand flexibility characteristic of chlorinated polyolefins, they are alsoused as hoses or sheets, packings, automobile constant velocityuniversal joint boots and the like. Such uses also require additionalproperties such as satisfactory heat resistance, ozone resistance,low-temperature rubber elasticity, compression set and fatigue strength.

Chlorinated polyolefins have conventionally been produced bychlorinating polyolefin powder in aqueous suspension while controllingthe reaction temperature, chlorine content, etc. Various proposals havebeen set forth for such aqueous suspension methods, in order to obtain auniform chlorinated polyolefin powder and in order to preventagglomerating during the chlorinated reaction and maintain the powderparticle size.

Surfactants or inorganic substances are commonly added asanti-aggregation agents in order to prevent agglomerating of particlesduring the reaction. On the other hand, when a copolymer of ethylene andan α-olefin is used as the starting material, a higher proportion of theα-olefin tends to result in lower crystallinity, and the increasednumber of free chains promotes agglomerating during the chlorinationreaction. A production method known as a solution to this problemcomprises a first step of chlorination at a temperature lower than thecrystal melting point of the polyolefin starting material, a second stepof heat treatment in the absence of chlorine at a temperature higherthan the crystal melting point, and a third step of chlorination up tothe final chlorine content at a temperature below the temperature of thesecond step and below the crystal melting point (see, for example,Japanese Unexamined Patent Publication No. 3-66325).

However, the effect of satisfactorily preventing agglomerating andmaintaining the powder particle size depends on preventing unwantedcrystal residue or a relatively poor level of non-uniformity, and it hasbeen difficult to achieve uniform chlorinated polyolefins with excellentproperties by the method described above.

It is also well known that polymerized polyolefin powder has a givenrange of particle size distribution and that differences in molecularweight and density are found between the particle sizes. The uniformityof a chlorinated polyolefin depends primarily on the uniformity of thepolyolefin starting material, and methods are known for obtaininguniform chlorinated polyethylene by adjusting the particle size of thepolyolefin starting material (see, for example, Japanese UnexaminedPatent Publication No. 8-59737).

However, while improvement toward a more uniform product is achieved bynarrowing the particle size distribution of the polyolefin powder, themore serious problem of variation within each particle is not affected,and these obtained chlorinated polyolefins therefore remainunsatisfactory in several of their properties.

DISCLOSURE OF INVENTION

It is therefore an object of the present invention to provide uniformchlorinated polyolefins which can give crosslinked rubbers andthermoplastic elastomers with excellent low-temperature rubberelasticity, compression set and fatigue strength, and a process fortheir production.

As a result of much diligent research directed toward solving theaforementioned problems, the present inventors have completed thepresent invention based on the discovery that these problems can beovercome by employing a production process wherein polyolefin powderhaving a mean particle size of no greater than 500 μm, obtained bypulverizing a melted and kneaded solid, is used as the starting materialfor chlorination.

Thus, the invention relates to the following (1) to (17).

(1) A process for production of a chlorinated polyolefin comprising astep of melting and kneading a polyolefin and then molding it to obtaina solid, a step of pulverizing the solid into powder having a meanparticle size of no greater than 500 μm, and a step of chlorinating thepowder.

(2) A process for production of a chlorinated polyolefin according to(1) above, wherein the chlorinating step further comprises a first stepof chlorination at above the crystal melting start temperature and morethan 10° C. below the crystal melting peak temperature of the polyolefinstarting material as determined by DSC, a second step of interruptingthe chlorine supply and performing heat treatment by heating to atemperature which is higher than 5° C. below the crystal melting peaktemperature, and a third step of rechlorination at a temperature abovethe crystal melting start temperature of the chlorinated polyolefinafter the heat treatment step.

(3) A process for production of a chlorinated polyolefin according to(1) or (2) above, wherein the polyolefin is polyethylene.

(4) A process for production of a chlorinated polyolefin according to(3) above, wherein the polyethylene is linear low-density polyethylene.

(5) A process for production of a chlorinated polyolefin according to(3) or (4) above, wherein the density of the polyethylene is 0.90-0.93.

(6) A process for production of a chlorinated polyolefin according toany one of (3) to (5) above, wherein the polyethylene is polyethylenewith a weight-average molecular weight (Mw) and number-average molecularweight (Mn) ratio (Mw/Mn) of no greater than 3.0 as measured by gelpermeation chromatography.

(7) A chlorinated polyolefin produced by a process according to any oneof (1) to (6) above, wherein the chlorinated polyolefin has a crystalheat of fusion of no greater than 30 J/g according to DSC.

(8) A chlorinated polyolefin according to (7) above, wherein thechlorine content is 15-45 wt %.

(9) A chlorinated polyolefin according to (7) or (8) above, wherein theelongation based on a tensile test is 1500% or greater, and the glasstransition temperature is no higher than −25° C.

(10) A chlorinated polyolefin according to any one of (7) to (9) above,wherein the chlorinated polyolefin is chlorinated polyethylene.

(11) A chlorinated polyolefin crosslinkable composition comprising 100parts by weight of a chlorinated polyolefin according to any one of (7)to (10) above, 0.5-20 parts by weight of an acid acceptor, 10-80 partsby weight of a reinforcer, 0.5-10 parts by weight of a crosslinkingagent and 5-70 parts by weight of a plasticizer.

(12) A crosslinked chlorinated polyolefin obtained by crosslinking achlorinated polyolefin crosslinkable composition according to (11)above.

(13) A crosslinked chlorinated polyolefin according to (12) above,wherein the temperature at which the relative modulus (RM)=2 by a coldflex test is no higher than −25° C.

(14) A crosslinked chlorinated polyolefin according to (12) above,wherein the temperature at which the relative modulus (RM)=5 by a coldflex test is no higher than −40° C.

(15) A crosslinked chlorinated polyolefin according to (12) above,wherein the temperature at which the relative modulus (RM)=10 by a coldflex test is no higher than −45° C.

(16) An automobile boot or hose employing a crosslinkable composition orcrosslinked polyolefin according to any one of (11) to (15) above.

(17) An industrial hose, sheet or packing employing a crosslinkablecomposition or crosslinked polyolefin according to any one of (11) to(15) above.

According to the present invention it is possible to provide chlorinatedpolyolefins which can be used as starting materials for crosslinkedrubbers and thermoplastic elastomers exhibiting excellentlow-temperature rubber elasticity, compression set and fatigue strength,which are particularly useful in the fields of automobiles, householdelectrical appliances, building materials and the like.

BEST MODE FOR CARRYING OUT THE INVENTION

The chlorinated polyolefin production process of the invention ischaracterized by comprising a step of melting and kneading a polyolefinand then molding it to obtain a solid, a step of pulverizing the solidinto powder having a mean particle size of no greater than 500 μm, and astep of chlorinating the powder.

Specifically, the production process is characterized by melting andkneading polyolefin powder or pellets, and then molding this into asolid which is then pulverized to a mean particle size of no greaterthan 500 μm to prepare a powder to be used as a starting material.

Here, the “solid” referred to here may be pellets, beads or the likeobtained by melting, kneading and molding, and although the size andshape or the like are not particularly restricted, a smaller size ispreferred because of the pulverization in the subsequent step. If themean particle size, represented as the 50% particle size based onweight, of the polyolefin powder used in the chlorination step of theprocess of the invention is greater than 500 μm, the low-temperaturerubber elasticity will be impaired.

The step of melting and kneading the polyolefin starting material andmolding it into a solid is usually carried out using an extruder or thelike, but there are no particular restrictions on the method so long asone or more starting materials selected from among powder obtained froma polyolefin production process and already melted, kneaded and moldedsolids, are first melted and subjected to a step of physical shearingfollowed by cooling to hardness to achieve the desired homogeneity ofthe molding material.

The melting and kneading of the polyolefin may also be carried out by anordinary method, and it will generally be conducted at or above themelting point of the polyolefin, but here as well, the process andconditions are not particularly restricted so long as the desiredhomogeneity of the molding material can be achieved.

The pulverization of the obtained solid is not particularly restricted,although a shearing-type pulverizer is more suitable for pulverizationof polyolefins than an impact-type pulverizer, and there are noparticular restrictions on the method or type of pulverizer used so longas the mean particle size of the powder after pulverization is nogreater than 500 μm.

As examples of polyolefins to be used for the invention there may bementioned α-olefin homopolymers of ethylene, propylene, butene-1,pentene-1, hexene-1, octene-1,4-methylpentene-1 and the like, andcopolymers of ethylene and α-olefin or copolymers of 2 or more differentα-olefins which are crystalline polymers. Such copolymers include randomand block copolymers. The polyolefins may be powders obtained from aproduction process or pellets obtained by prior melting and kneading,and two or more different polyolefins may be used in admixture for themelting and kneading.

The polyolefin is preferably polyethylene. Polyethylene for the purposeof the invention includes not only ethylene homopolymer but alsoethylene copolymer copolymerized with an α-olefin, such asmedium-density or linear low-density polyethylene. The polyethylene ispreferably linear low-density polyethylene, and the density of thepolyethylene is preferably 0.90-0.93. Also, the polyethylene preferablyhas a weight-average molecular weight (Mw) and number-average molecularweight (Mn) ratio (Mw/Mn) of no greater than 3.0 as measured by gelpermeation chromatography. The Mw/Mn ratio is more preferably between1.0 and 2.9, and especially between 1.5 and 2.8. If the Mw/Mn ratio isless than 1.0 the workability may be reduced, and if it exceeds 3.0 themechanical strength may be reduced.

As examples of polyolefins satisfying the conditions described abovethere may be mentioned those obtained by polymerization using ametallocene catalyst comprising a metallocene compound of a transitionmetal selected from Group IVB of the Periodic Table, and an organicaluminoxy compound. As examples of transition metals selected from GroupIVB of the Periodic Table there may be mentioned zirconium, titanium,hafnium and the like. As examples of organic aluminoxy compounds theremay be mentioned conventional known aluminoxanes obtained by reactionconducted by adding an organic aluminum compound such astrialkylaluminum to a compound containing water of adsorption or a saltcontaining water of crystallization, for example, aluminum sulfatehydrate or magnesium chloride hydrate suspended in an aromatichydrocarbon solvent, although there is no restriction to such compounds.

The step of chlorination of the powder preferably comprises a first stepof chlorination at above the crystal melting start temperature and morethan 10° C. below the crystal melting peak temperature of the polyolefinstarting material as determined by DSC, a second step of interruptingthe chlorine supply and performing heat treatment by heating to atemperature which is higher than 5° C. below the crystal melting peaktemperature, and a third step of rechlorination at a temperature abovethe crystal melting start temperature of the chlorinated polyolefinafter the heat treatment step.

In the first step of chlorination, chlorination at a temperature belowthe crystal melting start temperature will tend to promotenon-uniformity of chlorination and the resulting chlorinated polyolefinwill sometimes lack flexibility. On the other hand, chlorination at atemperature more than 10° C. below the crystal melting peak temperatureis preferred. Chlorimation at a higher temperature will tend to promoteaggregation and agglomerating of the reacting particles, resulting innon-uniform chlorination and often yielding a product withunsatisfactory elongation or low-temperature properties. Likewise, theheating in the second step at a temperature exceeding 5° C. below thecrystal melting peak temperature is preferred. If the heating is carriedout at a lower temperature, the crystals will tend to remain, often notonly making it difficult to obtain amorphous chlorinated polyethylenebut also resulting in non-uniformity even if crystalline chlorinatedpolyethylene is obtained. Similarly, chlorination in the third step at atemperature below the crystalline melting start temperature of thechlorinated polyolefin after the heat treatment step will also tend toresult in residue of the crystals, often not only making it difficult toobtain amorphous chlorinated polyethylene but also resulting innon-uniformity even if crystalline chlorinated polyethylene is obtained.

The chlorination step is preferably conducted so that the final chlorinecontent in the first step is no greater than 90%.

For chlorination by an aqueous suspension method, there may be addedconventional known agents, such as a dispersing agent to wet thepolyolefin powder and disperse it in water, or an anti-agglomeratingagent added either before or during the reaction for the purpose ofpreventing aggregation of the reaction particles during the chlorinationreaction.

As examples of dispersing agents there may be mentioned anionicsurfactants such as alkylbenzenesulfonates, alkylnaphthalenesulfonates,alkyldiphenylether sulfonates, dialkylsulfosuccinates, alkylphosphates,alkylsulfuric acid esters, naphthalenesulfonate formalin condensates andpolyoxyethylenealkylsulfuric acid esters, nonionic surfactants such assorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters,polyoxyethylene alkylallyl ethers, polyoxyethylenealkyl ethers andoxyethylene-oxypropylene block polymers, or polyvinyl alcohol,carboxymethylcellulose, starch, gelatin or the like.

As examples of anti-agglomerating agents there may be mentionedprotective colloids such as polyacrylic acid, copolymers of maleicanhydride and styrene or methylvinyl ether, or polyacrylamide,polyvinylpyrrolidone, or the like, surfactants such aspolystyrenesulfonate, sodium alkylallylsulfonate formalin condensate,diphenylmethylenesulfonic acid formalin condensate, isobutylene-styrenecopolymer sulfonic acid ester, β-naphthalenesulfonate formalincondensate and polyacrylates, or inorganic powders such as talc orsilica.

The crystals of the chlorinated polyolefin obtained by the productionprocess of the invention preferably have a crystal heat of fusion of nogreater than 30 J/g and more preferably no greater than 20 J/g accordingto DSC. The low-temperature rubber elasticity may be impaired when theheat of fusion according to DSC exceeds 30 J/g.

DSC is a method of measurement using a differential scanning calorimeter(JIS K7121 and K7122).

The chlorine content of the obtained chlorinated polyolefin ispreferably 15-45 wt %, more preferably 20-40 wt % and even morepreferably 25-35 wt %. If the chlorine content is less than 15 wt % orabove 45 wt %, the rubber elasticity, and especially the low-temperaturerubber elasticity, may be impaired.

The elongation of the chlorinated polyolefin based on a tensile test ispreferably 1500% or greater and more preferably 1600% or greater, andthe glass transition temperature is preferably no higher than −25° C.

A chlorinated polyolefin obtained by the production process of theinvention may be crosslinked as crosslinked rubber by being used in acomposition comprising basically an acid acceptor, a reinforcer, acrosslinking agent and a plasticizer. The crosslinking may beaccomplished by an ordinary method employing, for example, a press,injection molder, vulcanizer, hot air furnace or the like, selected asappropriate depending on the composition and the purpose of use.

The acid acceptor may be any one ordinarily used with chlorinatedpolyolefins. As examples there may be mentioned oxides or hydroxides ofcalcium, magnesium and the like, or synthetic hydrotalcite, syntheticzeolite or the like. These acid acceptors may be used alone or incombinations of two or more. The acid acceptor may be used in aproportion of 0.5-20 parts by weight and preferably 1-15 parts by weightto 100 parts by weight of the chlorinated polyolefin. If the acidacceptor is used at less than 0.5 part by weight the acid acceptingfunction will be insufficient, while if it is used at greater than 20parts by weight the obtained crosslinked rubber may have inferiormechanical strength.

As examples of reinforcers there may be mentioned carbon black, silica,calcium carbonate, talc, clay or the like. These may be used alone or incombinations of two or more. The reinforcer may be used in a proportionof 10-80 parts by weight and preferably 20-60 parts by weight to 100parts by weight of the chlorinated polyolefin. If the reinforcer is usedat less than 10 parts by weight the obtained crosslinked rubber may haveinferior mechanical strength, while if it is used at greater than 80parts by weight the flexibility may be impaired.

As examples of crosslinking agents there may be mentionedmercaptotriazine-based compounds, mercaptobenzothiadiazole-basedcompounds, organic peroxides and the like.

As examples of mercaptotriazine-based compounds there may be mentioned2,4,6-trimercapto-1,3,5-triazine, 1-methoxy-3,5-dimercaptotriazine,1-hexylamino-3,5-dimercaptotriazine,1-diethylamino-3,5-dimercaptotriazine,1-cyclohexylamino-3,5-dimercaptotriazine,1-dibutylamino-3,5-dimercaptotriazine and1-phenylamino-3,5-dimercaptotriazine.

Crosslinking accelerators may also be used in combination with thesemercaptotriazine-based compounds. As examples there may be mentionedbasic accelerators such as basic amine compounds, basic amine organicacid salts or addition products or diarylguanidine, sulfenamideaccelerators, thiuram accelerators, and the like.

As examples of mercaptobenzothiadiazole compounds there may be mentioned2,5-dimercapto-1,3,4-thiadiazole,5-mercapto-1,3,4-thiadiazole-2-thiobenzoate,1,3,4-thiadiazolyl-2,5-dithiobenzoate,5-mercapto-1,3,4-thiadiazole-2-thiostearate,5-mercapto-1,3,4-thiadiazole-2-thio-1-naphthoate,5-mercapto-1,3,4-thiadiazole-2-thiophenylacetate,5-mercapto-1,3,4-thiadiazole-2-thiocyclohexylcarboxylate,5-mercapto-1,3,4-thiadiazole-2-thio-p-toluate,5-mercapto-1,3,4-thiadiazole-2-thiocinnamate,2,5-di(butoxymethyl)-1,3,4-thiadiazole,2,2′-dimercapto-5,5′-dithiobis(1,3,4-thiadiazole) and2,2′-di(butoxymethyl)-5,5′-dithiobis(1,3,4-thiadiazole).

As examples of organic peroxides there may be mentioned ketone peroxide,peroxyketal, hydroperoxide, dialkyl peroxides, diacyl peroxide, peroxyesters and peroxy dicarbonate, and as specific examples there may bementioned 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, dicumylperoxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane,n-butyl-4,4-bis(t-butylperoxy)valerate andα,α′-bis(t-butylperoxy-m-isopropyl)benzene. These organic peroxides maybe used alone or in combinations of two or more.

Crosslinking aids may also be used in combination with these organicperoxides. As examples of useful crosslinking aids there may bementioned diallyl phthalate monomer, triallyl cyanurate, triallylisocyanurate, ethyleneglycol dimethacrylate, trimethylpropanetrimethacrylate and N,N′-m-phenylenebismaleimide. These coagents mayalso be used alone or in combinations of two or more.

The crosslinking agent may be used in a proportion of 0.5-10 parts byweight and preferably 1-5 parts by weight to 100 parts by weight of thechlorinated polyolefin. If the crosslinking agent is used at less than0.5 part by weight, crosslinking may be insufficient making itimpossible to achieve the intended crosslinked rubber properties. If itis used at greater than 10 parts by weight, the viscosity may increaseduring working, not only constituting a hindrance for molding but alsoresulting in inferior flexibility of the obtained crosslinked rubber.

As examples of plasticizers there may be mentioned phthalic esters suchas dibutyl phthalate, diethyl phthalate, diheptyl phthalate,di-2-ethylhexyl phthalate, di-n-octyl phthalate and dinonyl phthalate,aliphatic dibasic acid esters such as dimethyl adipate, diisobutyladipate, dibutyl adipate, di-2-ethylhexyl adipate, diisodecyl adipate,dibutyldiglycol adipate, di-2-ethylhexyl azelate, dimethyl sebacate,dibutyl sebacate, di-2-ethylhexyl sebacate and methylacetyl ricinoleate,and phosphoric acid esters such as trimethyl phosphate, triethylphosphate, tributyl phosphate, tri-2-ethylhexyl phosphate,tributoxyethyl phosphate, trioleyl phosphate, triphenyl phosphate,tricresyl phosphate, trixylenyl phosphate, cresyldiphenyl phosphate,xylenyldiphenyl phosphate and 2-ethylhexyldiphenyl phosphate. Theseplasticizers may also be used alone or in combinations of two or more.

The plasticizer may be used in a proportion of 5-70 parts by weight andpreferably 10-60 parts by weight to 100 parts by weight of thechlorinated polyolefin. If the plasticizer is used at less than 5 partsby weight the plasticizing effect may be inadequate, while if it is usedat greater than 70 parts by weight bleeding of the plasticizer mayoccur.

In addition to the basic composition described above, other componentsmay be appropriately added as necessary, such as stabilizers, flameretardants, pigments, antioxidants, ultraviolet absorbers, processingaids and the like, which are commonly used in crosslinked rubbers andplastics.

In a cold flex test described in JIS K6261-1993 (Vulcanized Rubber ColdFlex Test), the temperatures at which the relative modulus (RM) of theobtained crosslinked rubber is 2, 5 and 10 (t₂, t₅ and t₁₀) are ≦−25°C., ≦−40° C. and ≦−45° C., respectively, and preferably ≦−27° C., ≦−43°C. and ≦−49° C., respectively. The relative modulus is the value withrespect to the modulus at ordinary temperature (23±2° C.), and thesevalues are the temperatures for a 2-fold, 5-fold and 10-fold modulus,respectively. A lower temperature here reflects a lower hardeningtemperature and thus more excellent low-temperature properties asrubber, and it is common practice to select materials with reference tot₂, t₅ or t₁₀ depending on the purpose of use and the type of member.The numerical values are determined either from the modulus or the twistangle at numerous points as measured continuously from a lowtemperature; a difference of 2-3° C. in the relative modulus thus meansa higher modulus at each temperature in the low-temperature range andtherefore higher rigidity at low temperatures, and is thereforegenerally considered to be a major difference in terms of practical use.

The obtained crosslinked rubber maintains the heat resistance ofconventional chlorinated polyolefin-based crosslinked rubber, whileexhibiting a satisfactory balance between excellent low-temperaturerubber elasticity and high mechanical fatigue strength and compressionset, and it is therefore suitable for purposes including automobileparts, for example, boots such as constant velocity universal jointboots and hoses such as air cleaner hoses, or for industrial uses, forexample, as hoses, sheets, packings and the like.

The present invention will now be explained in greater detail throughexamples and comparative examples, with the understanding that theinvention is in no way limited by these examples.

The mean particle size was determined by measuring the filtered weightfraction by the Ro-Tap method using a wire sieve according to JIS Z8801,and recording the mean particle size as the particle size with a 50%cumulative weight percentage.

The melt flow rate (MFR) was measured at 190° C., according to JISK7210.

In order to determine the crystal heat of fusion, crystal melting starttemperature (Tms) and crystal melting peak temperature (Tmp), thecrystal heat of fusion was measured using a differential scanningcalorimeter according to JIS K7121 and K7122, and the melting starttemperature and peak temperature were read during the measurement.

The tensile strength and elongation were measured according to JISK6301. The Tg (glass transition temperature) was measured according tothe method described in Kobunshi Jikkengaku [Polymer Experiments] Vol.12, “Thermodynamic, electrical and optical properties” (KyoritsuPublishing Co., Ltd.), p. 74-77.

EXAMPLE 1

Pellets of polyethylene NF-364A (density: 0.920, Mw/Mn: 2.0) by JPO Co.,Ltd. (obtained by melting, kneading and pelleting polymerized powder)were pulverized to a mean particle size of 0.45 mm (450 μm) using aturbogrinder by Turbo Kogyo Co., Ltd.

Next, 80 L of water, 80 g of sodium alkyldiphenylethersulfonate as adispersing agent and 80 g of sodium polystyrenesulfonate as ananti-agglomerating agent were added to a 100 L autoclave, and 10 kg ofthe aforementioned pulverized polyethylene was loaded therein.

The first stage of chlorination was carried out to a chlorine content of15 wt % at 105° C. The chlorine gas supply was then interrupted, heatingto 127° C. was followed by cooling to 110° C., and a second stage ofchlorination was carried out to a chlorine content of 28 wt % at atemperature of 110° C. The chlorination was followed by water washingand drying by ordinary procedures to obtain chlorinated polyethylene.The crystal melting start temperature of the chlorinated polyethyleneafter the heat treatment step conducted between the first stage ofchlorination and the second stage of chlorination was 85° C.

A test piece was prepared by adding 2 parts by weight of dioctyltinmaleate and 1 part by weight of calcium stearate as stabilizers to 100parts by weight of the chlorinated polyethylene, kneading the mixturefor 5 minutes with a roll at 130° C. and then press molding a test pieceat a temperature of 170° C. and a pressure of 200 kg/cm².

EXAMPLES 2-9

Chlorination was carried out in the same manner as Example 1 using thestarting materials and conditions shown in Table 1, and the obtainedchlorinated polyethylene was used to fabricate a test piece in the samemanner as Example 1.

COMPARATIVE EXAMPLE 1

Chlorination was carried out in the same manner as Example 1 except thatpolyethylene powder with a mean particle size of 400 μm (polymerizedpowder without melting or kneading) was used as the starting materialwithout pulverization, and the obtained chlorinated polyethylene wasused to fabricate a test piece in the same manner as Example 1.

COMPARATIVE EXAMPLE 2

Chlorination was carried out using the same starting materials asExample 1 pulverized to 800 μm, and the obtained chlorinatedpolyethylene was used to fabricate a test piece in the same manner asExample 1.

COMPARATIVE EXAMPLES 3 AND 4

The polyethylene of the polyethylene pellets used in Example 6 butbefore pelleting (the polymerized powder) was used as the startingmaterial for Comparative Example 3 and the polyethylene of thepolyethylene pellets used in Example 7 but before pelleting (thepolymerized powder) was used as the starting material for ComparativeExample 4, without melting or kneading, and performing only particlesize adjustment by pulverization. The subsequent chlorination wascarried out under the same conditions as in the respective examples andtest pieces were fabricated. TABLE 1 First step Melt- ing/ Chlorinationstep conditions knead- Starting material properties First step Thirdstep ing Form Mean Degree of Second Tms Degree of before before MFRparticle Tempera- chlorina- step after Tempera- chlorina- pulver-pulver- Density Mw/ g/10 size Tms Tmp ture tion Tempera- second turetion ization ization g/cm³ Mn min μm ° C. ° C. ° C. wt % ture step ° C.wt % Example 1 yes pellet 0.920 2.0 1.0 450 75 126 105 15 127 85 110 28Example 2 yes pellet 0.920 2.0 1.0 420 75 126 105 15 127 86 110 28Example 3 yes pellet 0.920 2.0 1.0 100 75 126 105 15 127 88 105 28Example 4 yes pellet 0.920 2.0 1.0 100 75 126 105 15 127 88 110 28Example 5 yes pellet 0.920 2.0 4.0 400 74 125 105 15 126 87 110 28Example 6 yes pellet 0.912 2.5 2.0 440 71 124 105 15 125 86 110 28Example 7 yes pellet 0.930 2.6 1.0 400 73 125 105 15 126 87 110 28Example 8 yes pellet 0.920 2.0 1.0 450 75 126 110 10 127 88 110 28Example 9 yes pellet 0.920 2.0 1.0 450 75 126 105 15 127 85 115 28 Comp.Ex. 1 no powder 0.920 2.0 1.0 400 74 126 105 15 127 87 110 28 Comp. Ex.2 yes pellet 0.920 2.0 1.0 800 75 126 105 15 127 88 110 28 Comp. Ex. 3no powder 0.912 2.5 2.0 440 71 124 105 15 125 85 110 28 Comp. Ex. 4 nopowder 0.930 2.6 1.0 400 73 125 105 15 126 86 110 28

The test pieces obtained by the method described above were used formeasurement of properties such as crystal heat of fusion, tensilestrength, elongation and Tg. The results are shown in Table 2. TABLE 2Properties of chlorinated product Crystal Degree heat of of fusionchlorination M100 TB Elongation Tg J/g wt % MPa MPa % ° C. Example 1 1.028 1.20 6.06 ≧1600 −25 Example 2 1.0 28 1.05 4.97 ≧1600 −26 Example 3 1028 1.04 3.62 ≧1600 −25 Example 4 1.0 28 0.94 3.42 ≧1600 −26 Example 51.0 28 1.20 6.00 ≧1600 −25 Example 6 <0.1 28 0.85 5.54 ≧1600 −27 Example7 0.5 28 0.96 7.02 ≧1600 −25 Example 8 1.5 28 1.09 6.25 ≧1600 −25Example 9 <0.1 28 0.94 6.14 ≧1600 −26 Comp. Ex. 1 10 28 1.32 8.34 1200−22 Comp. Ex. 2 1.0 28 2.50 10.00 1000 −20 Comp. Ex. 3 1.0 28 1.24 6.061200 −23 Comp. Ex. 4 2.0 28 1.65 7.43 1100 −20

The chlorinated polyethylene products obtained in Examples 1 to 9 allhad elongation of 1600% or greater in the tensile test and a low 100%modulus, indicating high flexibility. Also, the glass transitiontemperatures were −25° C. or below, indicating satisfactorylow-temperature flexibility. On the other hand, the chlorinatedpolyethylene products obtained in the Comparative Examples 1 to 4 hadpoor flexibility and glass transition temperatures exceeding −25° C.,indicating poor low-temperature flexibility.

The following test was also conducted in order to examine the propertiesof the crosslinked rubber at low temperature.

To 100 parts by weight of the chlorinated polyethylene obtained in eachof the examples and comparative examples there were added 10 parts byweight of magnesium oxide (KYOWAMAG 150-1, product of Kyowa ChemicalIndustry Co., Ltd.), 50 parts by weight of carbon black (SHOBLACK MAF·G,product of Showa Cabot, KK.) and 40 parts by weight of a plasticizer(SANSOSAIZA-DOS, product of New Japan Chemical Co., Ltd.), and themixture was kneaded with a Banbury mixer. After then adding 2.5 parts byweight of 1,3,5-trithiocyanuric acid (TCA-D, product of OuchishinkoChemical Industrial Co., Ltd.) as a crosslinking accelerator and 1.5parts by weight of a dicyclohexylamine salt of 2-mercaptobenzothiazole(MDCA, product of Ouchishinko Chemical Industrial Co., Ltd.) as acrosslinking agent, the mixture was kneaded with a roll.

For further crosslinking, the kneaded mixture was pressed with a pressat 180° C. for 6 minutes and heated in an oven at 150° C. for 3 hours toobtain a sample.

The obtained crosslinked rubber samples were subjected to a cold flextest according to JIS K6261 (Vulcanized Rubber Cold Flex Test), and thet₂ temperature, t₅ temperature and t₁₀ temperature of the relativemodulus (RM) were calculated. For measurement of the mechanical fatigueproperty, pulling at a tension from 0-100% was repeated 10 million timesat a rate of 300 times/min using an elongation tester with 10 JIS #3dumbbells, and the number of broken samples was recorded. A smallernumber of broken samples indicates a superior mechanical fatigueproperty. The compressive set was also measured according to JIS K6301,with 25% compression at 100° C. for 70 hours.

The results are shown in Table 3. TABLE 3 Crosslinked rubber propertiesCold flex test Number of t₂ t₅ t₁₀ Freezing broken samples temperaturetemperature temperature point from mechanical Compression ° C. ° C. ° C.° C. fatigue (of 10) set % Example 1 −28 −43 −49 −62 0 29 Example 2 −32−45 −51 −64 0 24 Example 3 −28 −45 −50 −62 0 29 Example 4 −30 −46 −52−63 0 25 Example 5 −28 −44 −49 −61 0 26 Example 6 −33 −48 −55 −66 0 23Example 7 −30 −46 −51 −63 0 26 Example 8 −30 −46 −51 −63 0 24 Example 9−31 −47 −51 −64 0 27 Comp. Ex. 1 −24 −38 −42 −57 7 38 Comp. Ex. 2 −23−37 −41 −56 8 38 Comp. Ex. 3 −24 −39 −43 −58 10 36 Comp. Ex. 4 −21 −36−39 −52 5 37

The crosslinked rubbers of the chlorinated polyethylene obtained inExamples 1 to 9 had t₂, t₅ and t₁₀ temperatures of below −25° C., −40°C. and −45° C., respectively, in the cold flex test with the Gehmantester, indicating excellent low-temperature flexibility. Also, thecompression sets were below 30%, indicating a satisfactory balance withlow-temperature flexibility. The mechanical fatigue properties alsoindicated superior durability judging from the small number of brokensamples.

On the other hand, the crosslinked rubbers of Comparative Examples 1 to4 had t₂, t₅ and t₁₀ temperatures of or above −25° C., −40° C. and −45°C., respectively, in the cold flex test, indicating poor low-temperatureflexibility. Also, the compression sets were greater than 30%,indicating poor balance with low-temperature flexibility, and themechanical fatigue properties indicated inferior durability judging fromthe number of half or more broken samples.

INDUSTRIAL APPLICABILITY

The present invention provides chlorinated polyolefins which can be usedfor the production of crosslinked rubbers and thermoplastic elastomersuseful in the field of automobiles, household electrical appliances,building materials and the like.

1. A process for production of a chlorinated polyolefin comprising astep of melting and kneading a polyolefin and then molding it to obtaina solid, a step of pulverizing the solid into powder having a meanparticle size of no greater than 500 μm, and a step of chlorinating thepowder.
 2. A process for production of a chlorinated polyolefinaccording to claim 1, wherein the chlorinating step further comprises afirst step of chlorination at above the crystal melting starttemperature and more than 10° C. below the crystal melting peaktemperature of the polyolefin starting material as, determined by DSC, asecond step of interrupting the chlorine supply and performing heattreatment by heating to a temperature which is higher than 5° C. belowthe crystal melting peak temperature, and a third step of rechlorinationat a temperature above the crystal melting start temperature of thechlorinated polyolefin after the heat treatment step.
 3. A process forproduction of a chlorinated polyolefin according to claim 1 or 2,wherein the polyolefin is polyethylene.
 4. A process for production of achlorinated polyolefin according to claim 3, wherein the polyethylene islinear low-density polyethylene.
 5. A process for production of achlorinated polyolefin according to claim 3 or 4, wherein the density ofthe polyethylene is 0.90-0.93.
 6. A process for production of achlorinated polyolefin according to any one of claims 3 to 5, whereinthe polyethylene is polyethylene with a weight-average molecular weight(Mw) and number-average molecular weight (Mn) ratio (Mw/Mn) of nogreater than 3.0 as measured by gel permeation chromatography.
 7. Achlorinated polyolefin produced by a process according to any one ofclaims 1 to 6, wherein the chlorinated polyolefin has a crystal heat offusion of no greater than 30 J/g according to DSC.
 8. A chlorinatedpolyolefin according to claim 7, wherein the chlorine content is 15-45wt %.
 9. A chlorinated polyolefin according to claim 7 or 8, wherein theelongation based on a tensile test is 1500% or greater, and the glasstransition temperature is no higher than −25° C.
 10. A chlorinatedpolyolefin according to any one of claims 7 to 9, wherein thechlorinated polyolefin is chlorinated polyethylene.
 11. A chlorinatedpolyolefin crosslinkable composition comprising 100 parts by weight of achlorinated polyolefin according to any one of claims 7 to 10, 0.5-20parts by weight of an acid acceptor, 10-80 parts by weight of areinforcer, 0.5-10 parts by weight of a crosslinking agent and 5-70parts by weight of a plasticizer.
 12. A crosslinked chlorinatedpolyolefin obtained by crosslinking a chlorinated polyolefincrosslinkable composition according to claim
 11. 13. A crosslinkedchlorinated polyolefin according to claim 12, wherein the temperature atwhich the relative modulus (RM)=2 by a cold flex test is no higher than−25° C.
 14. A crosslinked chlorinated polyolefin according to claim 12,wherein the temperature at which the relative modulus (RM)=5 by a coldflex test is no higher than −40° C.
 15. A crosslinked chlorinatedpolyolefin according to claim 12, wherein the temperature at which therelative modulus (RM)=10 by a cold flex test is no higher than −45° C.16. An automobile boot or hose employing a crosslinkable composition orcrosslinked polyolefin according to any one of claims 11 to
 15. 17. Anindustrial hose, sheet or packing employing a crosslinkable compositionor crosslinked polyolefin according to any one of claims 11 to 15.